(a) Field of the Invention
The present invention relates to a device for improving the heating of a glass distribution channel, said device including a cylindrical duct whose upstream end is connected to means for feeding a premixture of air and fuel gas and whose downstream end opens inside a cylindrical bore into a refractory block which is inserted in a wall of the channel, said cylindrical bore having an extension consisting of a cylindrical axial duct of smaller diameter than said bore, the cylindrical duct being surrounded by a sealing ring which covers the face of the cylindrical bore into which said duct is inserted.
(b) Description of the Prior Art
A continuous glass production line comprises in succession a compounding shop where the mixture of the raw materials which are introduced into the melting oven is introduced, followed by a pre-basin in which the molten glass passes in order to be degasified, and one or more distribution channels connected to shaping machines. These distribution channels have dual purpose, i.e. transportation of the molten glass and temperature conditioning same.
Transportation of the molten glass is carried out by gravity and the latter flows at low speed, of the order of a few meters per hour.
Temperature conditioning of the glass is the most important function of the feeder, since it is responsable for the manufacture of a product of high and uniform quality. This conditioning function comprises for example three sub-functions:
Modification of the temperature of the molten glass: in general, cooling of the glass from the temperature of the oven to the shaping temperature (in certain cases heating up of the glass).
Uniformize the temperature of the glass, in order to limit transversal and vertical temperature gradients.
Control of the temperature of the glass sent to the shaping machines.
The first sub-function can be carried out in two different ways:
(1) The glass is abruptly cooled down during a short period of time after which its temperature is allowed to become uniform. This method requires internal cooling means, such as ventilation, water circulation, which reduce the true yield of the heating equipment provided for maintaining a sufficient level of temperature in the channel. Moreover, this technique requires some knowledge of the glass flow in the channel so as to prevent unnecessarily high transversal gradients of temperature.
(2) The glass is cooled down in a continuous and very slow manner. With this technique, it is only sufficient to rely on the natural cooling down resulting from the losses in the walls of the channel.
To realize the second sub-function (to uniformize the temperature of the glass), it is necessary to heat the marginal zones of the upper surface of the glass vein, because the exterior layers of this vein cool down much more rapidly than the core, since glass is a good insulating material and even in a mass of hot glass, the heat transfers are small. The burners used to reheat the marginal zones of the glass vein are generally supplied from a feed tank containing a premixture of cold air and of the fuel gas used, which presents some danger if the flame is put out.
To realize the third sub-function which is made necessary to obtain a uniform quality of the finished product, the channel comprises a plurality of successive zones whose heating is totally controlled from a unique temperature probe.
In a feeder intended for molten glass, the glass normally flows in a refractory channel whose sides and bottom portion are insulated, towards a feeding basin located upstream of the channel. For relatively small flows, heat is generally supplied by means of burners mounted in the lateral walls of the feeders in oder to try to maintain the glass in molten condition at the temperature required for distribution in the basin. At a higher flow, small amounts of heat may be applied selectively, and a removal of the heat is necessary for the increased flow as this is the case in the feeders presently built.
In order to save energy by reducing the size of the tank of nitrogen which is present in the fumes which are released by a burner and to increase the real temperature of the flame of a burner, it is known to mix oxygen with the fuel gas in a quantity which varies. Different well known methods can be considered for this addition of oxygen to a premixture of air and fuel gas:
The dilution which consists in mixing the additional oxygen in the duct which is used for feeding the mixture of air and fuel gas. The plurality of burners constituting a zone of the feeder would lead to problems of safety if pure oxygen would be introduced in the auxiliary tank containing the premixture, in view of the modifications of the limits of inflammability of the mixture, and the increase of the speed of combustion with respect to a reduction of the speed at which the mixture passes through the auxiliary tank and the burner. Indeed, if one volume of oxygen is introduced, the quantity of air must be reduced at the rate of 5 volumes, which means that the flow must be modified, i.e. the rate of flow of the mixture in the ducts. In practice, this solution is therefore not acceptable.
A second method consists in using a jet for injecting pure oxygen, i.e. the oxygen is introduced by means of a pipe which is separate from the pure oxygen burner and is located near the flame of the burner. This technique is particularly complicated, in view of the short distance between the burner and the glass bath which does not permit an easy mounting of the jets. This technique is also complicated due to the narrowness of the feeding channel which requires a rapid mixture of the flame and of oxygen, and to the important number of holes to be made in the lateral wall of the feeder to mount the jets therein. Consequently, such a solution requires important modifications in the existing installations.
A third method consists in using oxycombustible burners. However, the use of such burners requires a new design of the feeder to prevent the refractory elements from overheating, in view of the very high temperature which subsists at the base of the flame of the oxycombustible burners. Therefore, this solution cannot be adapted to the channels for feeding glass as they exist in the equipments which are now in operation.
Presently, we are therefore faced with the problem of using oxygen in the burners operating with air and fuel gas, mounted in the feeders, so as to utilize the existing equipments without modification, while benefiting from the improvements brought about by the use of an overoxygenated combustive material.